1. Field of the Invention
The present invention relates to storage area networks, and more particularly, to monitoring events in storage area networks.
2. Background of the Invention
Storage Area Networks (“SANs”) provide multiple paths to host computing systems to access memory devices (or storage devices). The multiple paths allow host systems to access data in the event of a failure.
Various standards are used for operating SANs. One such standard is Fibre Channel. Fibre channel is a set of American National Standard Institute (ANSI) standards, which provide a serial transmission protocol for storage and network protocols such as HIPPI, SCSI, IP, ATM and others. Fibre channel provides an input/output interface to meet the requirements of both channel and network users.
Fibre channel supports three different topologies: point-to-point, arbitrated loop and fibre channel fabric. The point-to-point topology attaches two devices directly. The arbitrated loop topology attaches devices in a loop. The fibre channel fabric topology attaches host systems directly to a fabric, which are then connected to multiple devices. The fibre channel fabric topology allows several media types to be interconnected.
Fibre channel is a closed system that relies on multiple ports to exchange information on attributes and characteristics to determine if the ports can operate together. If the ports can work together, they define the criteria under which they communicate.
In fibre channel, a path is established between two nodes where the path's primary task is to transport data from one point to another at high speed with low latency, performing only simple error detection in hardware.
Fibre channel fabric devices include a node port or “N_Port” that manages fabric connections. The N_port establishes a connection to a fabric element (e.g., a switch) having a fabric port or F_port. Fabric elements include the intelligence to handle routing, error detection, recovery, and similar management functions.
A fibre channel switch is a multi-port device where each port manages a simple point-to-point connection between itself and its attached system. Each port can be attached to a server, peripheral, I/O subsystem, bridge, hub, router, or even another switch. A switch receives messages from one port and automatically routes it to another port. Multiple calls or data transfers happen concurrently through the multi-port fibre channel switch.
Fibre channel switches use memory buffers to hold frames received and sent across a network. Associated with these buffers are credits, which are the number of frames a Fibre Channel port can transmit without overflowing the receive buffers at the other end of the link. Receiving an R_RDY primitive signal increases the credit, and sending a frame decreases the credit.
In conventional SAN systems, if an input/output operation is “timed out”, (i.e. it takes longer than say a threshold value) it results in an application time-out. This results in a prolonged recovery operation and reduces the overall availability of data to a user using a host computing system. Hence, in conventional systems, recovery occurs after a failure has already occurred.
As SANs become more complex with higher bandwidth requirements there is a need for detecting failure and re-routing data requests before the actual failure occurs and disrupts information flow within the SAN.